Immunological detection of fructose-derived advanced glycation end-products.

The advanced stage of non-enzymatic glycation (also called the Maillard reaction) that leads to the formation of advanced glycation end-products (AGEs) has an important function in the pathogenesis of angiopathy in diabetic patients. So far, most studies have been focused on the Maillard reaction by glucose. Although an elevated level of glucose had been thought to have a primary function in the Maillard reaction, on a molecular basis, glucose is among the least reactive sugars within biological systems. In addition to the extracellular formation of AGEs, rapid intracellular AGEs formation by various intracellular precursors (fructose, trioses, and dicarbonyl compounds) has recently attached attention. In this study, we considered the Maillard reaction with particular attention to the potential function of fructose. Fructose AGE-modified serum albumins were prepared by incubation of rabbit or bovine serum albumin (RSA or BSA) with D-fructose. After immunization of rabbits, fructose-derived AGEs (Fru-AGE) antiserum was subjected to affinity chromatography on a Sepharose 4B column coupled with Fru-AGE-BSA. Characterization of the novel anti-Fru-AGE antibody was performed with a competitive enzyme-linked immunosorbent assay and immunoblot analysis. The assay of Fru-AGE was established using the immunoaffinity-purified-specific antibody, and the presence of Fru-AGE in healthy and diabetic serum was shown (7.04+/-4.47 vs 29.13+/-18.08 U/ml). We also investigated whether high glucose treatment could stimulate intracellular Fru-AGE production in cultured pericytes, and we analyzed the amount of Fru-AGE contained in some common commercial beverages and condiments. It is possible that Fru-AGE formation by these endogenous and exogenous routes contributes importantly to the tissue pathology of diabetes and aging. This paper provides novel and clinically relevant information on the detection of Fru-AGE between fructose and proteins.

TAGE (toxic AGEs) theory in diabetic complications.

Diabetic complication is a leading cause of acquired blindness, end-stage renal failure, a variety of neuropathies and accelerated atherosclerosis. Chronic hyperglycemia is initially involved in the pathogenesis of diabetic micro- and macro-vascular complications via various metabolic derangements. High glucose increased production of various types of advanced glycation end-products (AGEs). Recently, we found that glyceraldehyde-derived AGEs (AGE-2) play an important role in the pathogenesis of angiopathy in diabetic patients. There is considerable interest in receptor for AGEs (RAGE) found on many cell types, particularly those affected in diabetes. Recent studies suggest that interaction of AGE-2 (predominantly structure of toxic AGEs; TAGE) with RAGE alters intracellular signaling, gene expression, release of pro-inflamatory molecules and production of reactive oxygen species (ROS) that contribute towards the pathology of diabetic complications. We propose three pathways for the in vivo formation of AGE-2 precursor, glyceraldehyde, such as i) glycolytic pathway, ii) polyol pathway, and iii) fructose metabolic pathway. Glyceraldehyde can be transported or can leak passively across the plasma membrane. It can react non-enzymatically with proteins to lead to accelerated formation of TAGE at both intracellularly and extracellularly. In this review, we discuss the molecular mechanisms of diabetic complications, especially focusing on toxic AGEs (TAGE) and their receptor (RAGE) system.

Involvement of advanced glycation end-products (AGEs) in Alzheimer's disease.

The advanced stage of the glycation process (one of the post-translational modifications of proteins) leads to the formation of advanced glycation end-products (AGEs) and plays an important role in the pathogenesis of angiopathy in diabetic patients. It has recently become clear that AGEs also influence physiological aging and neurodegenerative diseases such as Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS). Recently we have provided direct immunochemical evidence for the existence of six distinct AGE structures within the AGE-modified proteins and peptides that circulate in the serum of diabetic patients on hemodialysis (DM-HD). We showed a direct toxic effect of the synthetic AGE-2 (glyceraldehyde-derived AGEs) on cortical neuronal cells and provided evidence for a toxic effect of AGE-2 present in DM-HD serum. These results indicate that of the various types of AGE structures that can form in vivo, the AGE-2 structure is likely to play an important role in the pathophysiological processes associated with AGE formation. In AD brains, AGE-2 epitope was mainly present in the cytosol of neurons in the hippocampus and para-hippocampal gyrus. Protein cross-linking by AGE structures results in the formation of protease-resistant aggregates. Such protein aggregates may interfere with both axonal transport and intracellular protein traffic in neuron. In this review, we provide an outline of AGEs formation in vivo and propose that the novel structural epitope AGE-2 is an important toxic moiety for neuronal cells in AD.

Neurotoxicity of acetaldehyde-derived advanced glycation end products for cultured cortical neurons.

The Maillard reaction that leads to the formation of advanced glycation end products (AGEs) plays an important role in the pathogenesis of angiopathy in diabetic patients, in aging, and in neurodegenerative processes. We hypothesize that acetaldehyde (AA), one of the main metabolites of alcohol, may be involved in alcohol-induced neurotoxicity in vivo by formation of AA-derived AGEs (AA-AGEs) with brain proteins. Incubation of cortical neurons with AA-AGE produced a dose-dependent increase in neuronal cell-death, and the neurotoxicity of AA-AGE was neutralized by the addition of an anti-AA-AGE-specific antibody, but not by anti-N-ethyllysine (NEL) antibody. The AA-AGE epitope was detected in human brain of alcoholism. We propose that the structural epitope AA-AGE is an important toxic moiety for neuronal cells in alcoholism.